Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter. Some of these terms are defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11 specification but it should be appreciated that the invention is not limited to systems and methods complying with the IEEE 802.11 specification.
The term “Wi-Fi” is used to refer to technology that allows communication devices to interact wirelessly based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. The wireless communication may use microwave bands, e.g. in the 2.4 GHz to 5 GHz range.
The term “AP” is an acronym for Access Point and is used herein to define a device that allows wireless devices (known as User Equipment or “UE”) to connect to a wired network using Wi-Fi, or related standards. The AP usually connects to a router (via a wired network) as a standalone device, but it can also be an integral component of the router itself.
The term “UE” is an acronym for User Equipment(s) and is an example of a station, e.g. Wi-Fi station (STA) that may attach to an AP.
The term “associated STA” as used herein refers to a STA that is served by a certain AP, for example with a certain Service Set Identifier (SSID).
The term “station” or STA is a term used for any participant on the network, for example as used in the 802.11 specification. Both UEs and APs are considered in this context to be examples of stations. In the following the abbreviation STA is used for stations whose packets are detected by a Wi-Fi RDN station implementing embodiments of the invention.
BSS is acronym for Basic Service Set, which is typically a cluster of Stations associated with an AP dedicated to managing the BSS. A BSS built around an AP is called an infrastructure BSS. The term “backhaul” is used in the following to denote a communication path between two APs or base stations, for example using a different protocol from that used for wireless communication between an AP or base station and supported equipment or STA. The 802.11 specification does not provide for communication between APs. A backhaul link may operate outside a wireless, e.g. Wi-Fi, environment in which APs or base stations and associated UEs or other STAs are operating, or use one or more different channels from those used by APs to communicate with their associated stations. A backhaul link may use any combination of wired and wireless communication including but not limited to a cellular communication network, Ethernet, and the internet.
“Beacon transmission” refers to periodical information transmission which may include system information.
HT-LTF is an acronym for high throughput long training field as defined in the 802.11 specification.
MPDU is an acronym for media access code (MAC) protocol data unit as defined in the 802.11 specification.
NAV is an acronym for network allocation vector as defined in the 802.11 specification.
NDP is an acronym for null data packet.
PPDU is an acronym for physical layer convergence procedure (PLCP) protocol data unit as defined in the 802.11 specification.
The term “sounding” refers to a channel calibration procedure involving the sending of a packet, called a “sounding packet” from one participant on a network to another, for example as defined in the 802.11 specifications.
VHT is an acronym for very high throughput as defined in the 802.11 specification.
The specific Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) mechanism used in the 802.11 Media Access Control (MAC) is referred to as the distributed coordination function (DCF). A station that wishes to transmit first performs a clear channel assessment (CCA) by sensing the medium for a fixed duration, the DCF inter-frame space (DIFS).
SIFS, Short Inter Frame Space, as defined in the 802.11 specifications is the period between reception of the data frame and transmission of the ACK. SIFS is shorter than DIFS.
The term Clear Channel Assessment (CCA) as used herein refers to a CCA function, e.g. as defined in the 802.11 specification.
The term “MIMO” is an acronym for multiple input multiple output and as used herein, is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the transmit power over the antennas to achieve spatial multiplexing that improves the spectral efficiency (more bits per second per Hz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading), or increased antenna directivity.
“Channel estimation” is used herein to refer to estimation of channel state information (CSI) which describes properties of a communication link such as signal to noise ratio “SNR” and signal to interference plus noise ratio “SINR”. Channel estimation may be performed by user equipment or APs as well as other components operating in a communications system.
The term “beamforming” sometimes referred to as “spatial filtering” as used herein, is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity. The operation of attempting to achieve destructive interference in order to cancel a signal in a particular direction or angle is referred to as “nulling”. Complete cancellation of a signal is not usually achieved in practice and a “null” in a radiation pattern may refer to a minimum in signal strength. The lower the signal strength, the “deeper” the null is said to be.
The term “beamformer” as used herein refers to analog and/or digital circuitry that implements beamforming and may include combiners and phase shifters or delays and in some cases amplifiers and/or attenuators to adjust the weights of signals to or from each antenna in an antenna array. Digital beamformers may be implemented in digital circuitry such as a digital signal processor (DSP), field-programmable gate array (FPGA), microprocessor or the central processing unit “CPU” of a computer to set the weights as may be expressed by phases and/or amplitudes of the above signals. Various techniques are used to implement beamforming including: Butler matrices, Blass Matrices and Rotman Lenses. In general, most approaches may attempt to provide simultaneous coverage within a sector using multiple beams.